Abstract
At almost of all the meteorological stations in Japan, the 10 minutes averaged windspeed which has a probability of 1/50 of being exceeded in any one year was evaluated using the method due to Gumbel. This value was converted into one measured at 10 m above open, flat, level land for the purpose of eliminating the surface roughness influence. The map of Japan with isotachs of' basic windspeed' was drawn. The map has ironed out variations of windspeeds due to the small scale topographic influences. Finally, the map of Japan showing 'basic design windspeed' was proposed.
